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STRTOK(3) Linux Programmer's Manual STRTOK(3)


     strtok, strtok_r - extract tokens from strings


     #include <string.h>
     char *strtok(char *str, const char *delim);
     char *strtok_r(char *str, const char *delim, char **saveptr);
 Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
     strtok_r(): _POSIX_C_SOURCE
         || /* Glibc versions <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE


     The  strtok()  function breaks a string into a sequence of zero or more
     nonempty tokens.  On the first call  to  strtok(),  the  string  to  be
     parsed should be specified in str.  In each subsequent call that should
     parse the same string, str must be NULL.
     The delim argument specifies a set of bytes that delimit the tokens  in
     the  parsed  string.  The caller may specify different strings in delim
     in successive calls that parse the same string.
     Each call to strtok() returns a pointer  to  a  null-terminated  string
     containing the next token.  This string does not include the delimiting
     byte.  If no more tokens are found, strtok() returns NULL.
     A sequence of calls to strtok() that operate on the same  string  main-
     tains a pointer that determines the point from which to start searching
     for the next token.  The first call to strtok() sets  this  pointer  to
     point  to the first byte of the string.  The start of the next token is
     determined by scanning forward for the next nondelimiter byte  in  str.
     If  such  a  byte is found, it is taken as the start of the next token.
     If no such byte is found, then there are no more tokens,  and  strtok()
     returns NULL.  (A string that is empty or that contains only delimiters
     will thus cause strtok() to return NULL on the first call.)
     The end of each token is found by scanning  forward  until  either  the
     next  delimiter byte is found or until the terminating null byte ('\0')
     is encountered.  If a delimiter byte is found, it is overwritten with a
     null  byte to terminate the current token, and strtok() saves a pointer
     to the following byte; that pointer will be used as the starting  point
     when  searching  for  the next token.  In this case, strtok() returns a
     pointer to the start of the found token.
     From the above description, it follows that a sequence of two  or  more
     contiguous  delimiter  bytes in the parsed string is considered to be a
     single delimiter, and that delimiter bytes at the start or end  of  the
     string  are  ignored.  Put another way: the tokens returned by strtok()
     are always nonempty strings.   Thus,  for  example,  given  the  string
     "aaa;;bbb,",  successive  calls  to strtok() that specify the delimiter
     string ";," would return the strings "aaa" and "bbb", and then  a  null
     The  strtok_r()  function is a reentrant version strtok().  The saveptr
     argument is a pointer to a char * variable that is used  internally  by
     strtok_r()  in  order to maintain context between successive calls that
     parse the same string.
     On the first call to strtok_r(), str should point to the string  to  be
     parsed,  and the value of saveptr is ignored.  In subsequent calls, str
     should be NULL, and saveptr should  be  unchanged  since  the  previous
     Different  strings  may be parsed concurrently using sequences of calls
     to strtok_r() that specify different saveptr arguments.


     The strtok() and strtok_r() functions return  a  pointer  to  the  next
     token, or NULL if there are no more tokens.


     For   an   explanation   of   the  terms  used  in  this  section,  see
     |Interface  | Attribute     | Value                 |
     |strtok()   | Thread safety | MT-Unsafe race:strtok |
     |strtok_r() | Thread safety | MT-Safe               |


            POSIX.1-2001, POSIX.1-2008, C89, C99, SVr4, 4.3BSD.
            POSIX.1-2001, POSIX.1-2008.


     Be cautious when using these functions.  If you do use them, note that:
  • These functions modify their first argument.
  • These functions cannot be used on constant strings.
  • The identity of the delimiting byte is lost.
  • The strtok() function uses a static buffer while parsing, so it's not

thread safe. Use strtok_r() if this matters to you.


     The program below uses nested loops that employ strtok_r() to  break  a
     string  into  a  two-level hierarchy of tokens.  The first command-line
     argument specifies the string to be parsed.  The second argument speci-
     fies  the  delimiter  byte(s)  to  be used to separate that string into
     "major" tokens.  The third argument specifies the delimiter byte(s)  to
     be used to separate the "major" tokens into subtokens.
     An example of the output produced by this program is the following:
         $ ./a.out 'a/bbb///cc;xxx:yyy:' ':;' '/' 1: a/bbb///cc
                  --> a
                  --> bbb
                  --> cc 2: xxx
                  --> xxx 3: yyy
                  --> yyy
 Program source
      #include <stdio.h> #include <stdlib.h> #include <string.h>
     int main(int argc, char *argv[]) {
         char *str1, *str2, *token, *subtoken;
         char *saveptr1, *saveptr2;
         int j;
         if (argc != 4) {
             fprintf(stderr, "Usage: %s string delim subdelim\n",
         for (j = 1, str1 = argv[1]; ; j++, str1 = NULL) {
             token = strtok_r(str1, argv[2], &saveptr1);
             if (token == NULL)
             printf("%d: %s\n", j, token);
             for (str2 = token; ; str2 = NULL) {
                 subtoken = strtok_r(str2, argv[3], &saveptr2);
                 if (subtoken == NULL)
                 printf(" --> %s\n", subtoken);
         exit(EXIT_SUCCESS); }
     Another   example  program  using  strtok()  can  be  found  in  getad-


     index(3),  memchr(3),  rindex(3),  strchr(3),  string(3),   strpbrk(3),
     strsep(3), strspn(3), strstr(3), wcstok(3)


     This  page  is  part of release 4.16 of the Linux man-pages project.  A
     description of the project, information about reporting bugs,  and  the
     latest     version     of     this    page,    can    be    found    at

GNU 2017-09-15 STRTOK(3)

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